A portable electronic device, such as a selective call receiver or a cellular telephone, typically has a liquid crystal display (LCD) screen for displaying visual information. Conventionally, the visual information is obtained from processing data received from input devices such as a keyboard. It is also common to use the LCD screen as an input device in order to reduce space required by the keyboard and to make the portable electronic device easier to use.
Receiving inputs from an LCD screen require detection panels on the LCD screen to sense, for example, movements of a stylus-shaped apparatus inscribing information on the surface of the LCD screen. These movements, converted to voltage or pressure variations by electronic circuitry coupled to the detection panels, are typically processed by an analog to digital converter (ADC) to provide data for deriving the visual information.
Conventionally, a controller within the portable electronic device is dedicated to control the detection panels and the circuitry coupling to the detection panels. The controller sets the detection panels and the electronic circuitry to scan the LCD screen at a predetermined sampling frequency. As is known in the art, scanning in portable electronic devices unnecessarily consumes power when no inputs are received. Furthermore, as portable electronic devices operate with batteries having limited energy content, reducing or eliminating unnecessary power consumption prolongs the operating duration of such portable electronic devices.
Thus, what is needed is a method for an LCD screen to detect inputs efficiently and thereby reduce power consumption in a portable electronic device with the LCD screen.